The concept of generating and communicating with noise codes of the type termed "code mates" having autocorrelation functions which upon detection in a matched filter provide an impulse autocorrelation function is generally known and shown, for example, in U.S. Pat. No. 3,519,746, entitled, "Means And Method To Obtain An Impulse Autocorrelation Function", which issued to Frank S. Gutleber, the present inventor, on July 7, 1970. Other examples include U.S. Pat. No. 3,634,765, entitled, "System To Provide An Impulse Autocorrelation Function Upon Linear Addition . . .", which issued to Frank S. Gutleber on Jan. 11, 1972, and U.S. Pat. No. 4,293,953, entitled, "Bi-Orthogonal PCM Communication System Employing Multiplexed Noise Codes", which issued to Frank S. Gutleber, on Oct. 6, 1981. It is to this type of apparatus to which the present invention is generally directed.
Accordingly, it is an object of the present invention to provide an improvement in the generation and utilization of noise codes.
Another object of the invention is to provide an improvement in noise codes comprised of code mate pairs having autocorrelation functions which upon detection in a matched filter compress to an impulse.
Still another object of the invention is to provide multiplexed code mate pairs having more than one amplitude level.
These and other objects are achieved by multiplexed noise code mate pairs comprising a pair of bi-polar digital noise code mates having more than one amplitude level. Generated and utilized are code mate pairs of at least two code bits each wherein one code mate is comprised of two signal bits of first and second polarities, one bit of which has a larger amplitude than the other bit and wherein the other code mate is comprised of two signal bits of said second polarity, one bit of which has a like larger amplitude than the other bit. For example, where one code mate comprises a code a=1, 0.sup.K, the other code mate comprises a code b=0.sup.K, 0 or 0, 0.sup.K and where K is an amplitude multiplying term, 0 represents a positive pulse of unit amplitude and 1 represents a negative pulse of unit amplitude.